Many processes such as the Citrate process involve an absorption solution where sulfur dioxide is absorbed from the gas stream, and where hydrogen sulfide is added to the absorption solutions to form sulfur by the reaction EQU 2H.sub.2 S + SO.sub.2 .revreaction. 3S.degree. + 2H.sub.2 O. (1)
the process which has a continuous demand for hydrogen sulfide can readily be met by the sulfur formed in the reaction.
One method for producing hydrogen sulfide from the sulfur has been described in the "Canadian Mining and Metallurgical Bulletin", October 1957, page 614 and following. This involved the non-catalytic direct reaction of hydrogen with sulfur to form hydrogen sulfide at temperatures from 820.degree. to 1000.degree. F.
An admitted deficiency in the process is that reaction products are highly corrosive. Type 316 stainless steel, for instance, suffers severe corrosion. Another deficiency of the process is that hydrogen of high purity is required, and this is expensive.
In addition, unreacted sulfur vapor in the hot gases causes fouling and plugging of condensers when the gas stream is cooled to the dew point of water to enable the hydrogen sulfide to react with sulfur dioxide in the aqueous phase.
In the January 1970 edition of "Mining Engineering" at page 75 and following, there was published a Bureau of Mines Process for producing hydrogen sulfide. The first stage of the reaction occurs at a temperature of 600.degree. to 700.degree. C (1112.degree. to 1292.degree. F) using alumina as the catalyst where methane and sulfur react to form hydrogen sulfide by the principal reaction: EQU CH.sub.4 + 4S .revreaction. 2H.sub.2 S + CS.sub.2. (2)
the second stage reaction is at a temperature of 200.degree. to 300.degree. C (392.degree. to 572.degree. F) where carbon disulfide reacts with water to form hydrogen sulfide and carbon dioxide by the principal reaction: EQU CS.sub.2 + H.sub.2 O .fwdarw. 2H.sub.2 S + CO.sub.2. (3)
in addition to sharing the serious corrosion problems with the previously described process as represented by the mixture of sulfur and hydrogen sulfide at temperatures in excess of 900.degree. F, the carbon disulfide is formed initially in high amounts. When lower temperatures are used in the succeeding step the approach to a new equilibrium is poor because carbonyl sulfide and carbon disulfide only hydrolyze slowly to hydrogen sulfide. Thus, the unconverted carbon disulfide and any carbonyl sulfide formed are inert and represent a pollution problem in any process where the hydrogen sulfide is used.